1. Field of the Invention
This invention relates generally to electrochemical cells and, more particularly, this invention relates to a reactive metal/aqueous electrolyte electrochemical cell including means for stabilizing the electrolyte concentration.
2. Description of the Prior Art
The use of lithium and other highly reactive metals, such as so-called "light metals", as anode materials in electrochemical cells is well known. See for example, Rowley U.S. Pat. No. 3,791,871 (Feb. 24, 1974), the disclosure of which is incorporated herein by reference. Electrical energy is provided by the electrochemical reaction of the anodic metal with an aqueous electrolyte.
Often, an oxidizer such as hydrogen peroxide is present in the cell, and the overall reaction can be written, in the case of a lithium anode, as follows: EQU 2Li+H.sub.2 O.sub.2 .fwdarw.2LiOH(aq)
Where an air cathode is employed the reaction can be written: EQU 2Li+H.sub.2 O+1/2O.sub.2 (atm).fwdarw.2LiOH(aq)
As indicated in the foregoing equations, the anodic reaction product in lithium/aqueous electrolyte cells is lithium hydroxide. Optimally (at typical operation temperatures), the concentration of lithium hydroxide in the electrolyte is maintained at about 4.2 molar. As the lithium hydroxide concentration rises, power diminishes correspondingly, and passivation of the anode occurs if the electrolyte becomes saturated with lithium hydroxide.
Therefore, steps must be taken to maintain the lithium hydroxide concentration in the electrolyte at a level at which useful electrical current is produced.
For example, water can be added to dilute the electrolyte. This method can be especially advantageous in marine environments where water is plentiful. In non-marine environments water for dilution must be carried with the cell. This added weight diminishes the energy output per unit weight of the cell
Precipitation of the hydroxide by cooling or by the use of precipitants is possible but generally results in the formation of LiOH.H.sub.2 O. One water molecule is removed from the system for each lithium hydroxide molecule, necessitating the provision of extra water, thereby increasing the weight of the cell.